Three-dimensional object building apparatus and method for building three-dimensional object

ABSTRACT

The three-dimensional object building apparatus includes a powder delivering unit that delivers a powder on an object building area, a powder flattening device that flattens the powder delivered from the powder delivering unit to form a powder layer, and a light beam radiating unit that is disposed above the object building area and radiates a light beam on the powder layer to sinter or melt solidify the powder for building an object. The three-dimensional object building apparatus also includes a transferring mechanism that moves the light beam radiating unit in three-dimensional directions, and a shroud that moves integrally with the light beam radiating unit and surrounds a space above an area of the powder layer that is smaller than the object building area around a radiation of the light beam. The powder delivering unit and the powder flattening device move integrally with the light beam radiating unit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the foreign priority benefit under 35 U.S.C.§119 of Japanese Patent Application No. 2012-280834 filed on Dec. 25,2012, the disclosure of which is incorporated herein in its entirety byreference.

TECHNICAL FIELD

The present invention relates to a three-dimensional object buildingapparatus and a method for building a three-dimensional object, in whichan object is built by sintering a powder with a light beam.

BACKGROUND ART

In a conventional three-dimensional object building apparatus (SLM(Selective Laser Melting) apparatus), which is known for example asshown in Patent Document 1, a scanner for radiating a laser beam isprovided above the object building table (the work piece platform inPatent Document 1) on which an object is put. In order to enlarge thesize of the object to be built, a scanner is generally fixed on a X-Ydrive axis device such as a gantry (the cross-slide support in PatentDocument 1) so as to be movable in the directions of X and Y axes.

PRIOR TECHNICAL DOCUMENT Patent Document

[Patent Document 1] Japanese Patent Application Laid-Open PublicationNo. 2004-516166 (which corresponds to WO 2002/036330)

SUMMARY OF THE INVENTION Technical Problem

The technology of Patent Document 1 prolongs a time to conduct a powderdelivering process and a powder smoothing process, and therefore tendsto prolong a cycle time of object building. Moreover, because theapparatus is configured such that the whole chamber (space) for objectbuilding above the object building table is filled with an inert gasatmosphere, a consumption amount of the inert gas increases, and thecost for object building tends to increase.

The present invention has been created to solve the above problem, andits purpose is to provide a three-dimensional object building apparatusand a method of building a three-dimensional object, which cansuccessfully shorten the object building cycle time and reduce theconsumption amount of the ambient gas such as inert gas.

Solution to Problem

To solve the above problem, the present invention is a three-dimensionalobject building apparatus comprising: a powder delivering unit thatdelivers a powder on an object building area; a powder flattening devicethat flattens the powder delivered from the powder delivering unit toform a powder layer; a light beam radiating unit that is disposed abovethe object building area and radiates a light beam on the powder layerto sinter or melt solidify the powder for building an object; atransferring mechanism that moves the light beam radiating unit inthree-dimensional directions; a cover that moves integrally with thelight beam radiating unit and covers a space above an area of the powderlayer that is smaller than the object building area around a radiationof the light beam; wherein the powder delivering unit and the powderflattening device move integrally with the light beam radiating unit.

According to this three-dimensional object building apparatus, theadvantages described below are achieved.

(1) The size of the object to be built can be easily enlarged up to thethree-dimensional range of movement of the transferring mechanism thatholds the light beam radiating unit.

(2) The cycle time of object building can be shortened, because thepowder delivering unit and the powder flattening device are configuredintegrally with the light beam radiating unit so that a powder layer canbe formed at the time of movement of the light beam radiating unit.

(3) The apparatus can be configured compact, because the powderdelivering unit and the powder flattening device are configuredintegrally with the light beam radiating unit so that drive sources forrespective operations of the powder delivering unit and the powderflattening device become unnecessary.

(4) The consumption amount of the ambient gas can be reduced, becausethe ambient gas is supplied only to the inside of the cover that coversthe powder layer, the area of which is smaller than the object buildingarea.

(5) Since the light beam radiating unit is configured integrally withthe powder delivering unit and the powder flattening device, thedimensional precision is improved between the light beam radiating unitand the surface of a powder layer formed by the powder delivering unitand the powder flattening device. Accordingly, the focal point of alight beam at the powder layer becomes stable, and the precision ofobject building is improved.

(6) The cycle time of object building can be further shortened, becausethe object can be built by radiating a light beam while the light beamradiating unit is brought by the transferring mechanism.

Moreover, the apparatus may be configured such that the powderdelivering unit and the powder flattening device are disposed on a sideof the cover facing in a direction of forward movement.

According to this three-dimensional object building apparatus, thepowder delivering unit and the powder flattening device can beconfigured integrally with the cover with a simple structure.

Moreover, the apparatus may be configured such that the powderdelivering unit comprises a powder storage tank with a powder droppingopening formed at a lower portion thereof, and the powder flatteningdevice comprises a blade disposed between the powder storage tank andthe cover.

According to this three-dimensional object building apparatus, thepowder delivering unit and the powder flattening device can be made ofmembers having simple structures and thereby can be attached to thecover easily.

Moreover, the apparatus may further comprise an open-close door thatopens and closes the powder dropping opening of the powder storage tank.

According to this three-dimensional object building apparatus, deliveryof the powder from the powder storage tank can be easily controlled byopening and closing operation of the open-close door.

Moreover, the apparatus may be configured such that the cover comprisesan ambient-gas supplying port for supplying an ambient gas into aninside of the cover and a fume suction port for suctioning a fumegenerated in the inside of the cover.

According to this three-dimensional object building apparatus, theambient gas can be easily supplied to the inside of the cover and thefume can be easily ejected outside.

Moreover, the apparatus may be configured such that the cover isprovided with a skirt member that is movable vertically and blocks a gapmade between a lower end of the cover and the powder layer when lowereddown.

According to this three-dimensional object building apparatus, leakageof the ambient gas from the gap made between the cover and the powderlayer can be prevented efficiently.

Moreover, in the present invention, the method comprises a step forproviding a powder delivering unit, a powder flattening device, a lightbeam radiating unit and a cover structured integrally with one anothersuch that these are movable in three-dimensional directions, wherein thepowder delivering unit delivers a powder on an object building area, thepowder flattening device flattens a surface of the powder delivered fromthe powder delivering unit to form a powder layer, the light beamradiating unit is disposed above the object building area and radiates alight beam on the powder layer to sinter or melt solidify the powder forbuilding the object, the cover surrounds a space above an area of thepowder layer that is smaller than the object building area around aradiation of the light beam; a one-layer building step comprising apowder layer forming step for moving the cover in lateral direction sothat a powder of amount corresponding to the moved distance is deliveredby the powder delivering unit below the cover and flattened by thepowder flattening device, an object building step for radiating a lightbeam on the layer flattened in the powder layer forming step forbuilding the object, wherein one powder layer is built by repeating thepowder layer forming step and the object building step; wherein thethree-dimensional object is built by repeating uplifting the cover andthe one-layer building step.

According to this method of building a three-dimensional object, thesame advantages as aforementioned (1) to (5) can be obtained.

Moreover, the method may comprise the step of building athree-dimensional makeshift wall surrounding a space around the objectfor preventing collapse of the powder in the space around the object tobe built.

According to this method of building a three-dimensional object,collapse of the powder surrounding the object can be prevented by themakeshift wall

Advantageous Effects of Invention

According to the present invention, shortening the object building cycletime and reducing the consumption amount of the ambient gas such asinert gas can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a three-dimensional object building apparatusaccording to an embodiment of the present invention;

FIG. 2 is an exterior perspective view of a three-dimensional objectbuilding apparatus according to the embodiment;

FIG. 3A is a diagram for explaining an operation of thethree-dimensional object building apparatus according to the embodiment;

FIG. 3B is a diagram for explaining the operation of thethree-dimensional object building apparatus according to the embodiment;

FIG. 3C is a diagram for explaining the operation of thethree-dimensional object building apparatus according to the embodiment;

FIG. 4A is a diagram for explaining the operation of thethree-dimensional object building apparatus according to the embodiment;

FIG. 4B is a diagram for explaining the operation of thethree-dimensional object building apparatus according to the embodiment;

FIG. 4C is a diagram for explaining the operation of thethree-dimensional object building apparatus according to the embodiment;

FIG. 5A is a diagram for explaining the operation of thethree-dimensional object building apparatus according to the embodiment;

FIG. 5B is a diagram for explaining the operation of thethree-dimensional object building apparatus according to the embodiment;

FIG. 6 is a side view of the three-dimensional object building apparatuswhen a makeshift wall is built;

FIG. 7A is a side view of a variant structural example of an open-closedoor of the storage tank; and

FIG. 7B is a side view of the variant structural example of theopen-close door of the storage tank.

DETAILED DESCRIPTION

In FIG. 1, a three-dimensional object building apparatus 1 according tothe present embodiment is configured to mainly comprise: an objectbuilding bed 2; a powder delivering unit 3 which delivers a powder on anobject building area P₁ of the object building bed 2; a powderflattening device 4 which flattens the powder delivered from the powderdelivering unit 3 to form a powder layer 13; a light beam radiating unit5 which is disposed above the object building area P₁ and radiates alight beam L on the flattened powder layer 13 to either sinter or meltsolidify the powder in order to build an object; a transferringmechanism 6 which moves the light beam radiating unit 5 inthree-dimensional directions; a cover (hereinafter referred to as“shroud”) 7 which surrounds a space above an area of the powder layer 13that is smaller than the object building area P₁ around radiation of thelight beam L; and a controller 8. The shroud 7, the powder deliveringunit 3 and the powder flattening device 4 move integrally with the lightbeam radiating unit 5.

[Object Building Bed 2]

The object building bed 2 is a plate-shaped member disposed horizontallyinside an apparatus frame 9 formed for example in a shape of arectangular box, and is secured on an apparatus frame 9. A trolley 10for collecting a residual powder is placed below the object building bed2. The residual powder generated on the object building bed 2 iscollected by the trolley 10 via an ejection passage (not shown) which isbored through the object building bed 2 vertically, for example. Anobject placement plate 11 is detachably fitted into one part of an uppersurface of the object building bed 2 so as to be flush with the objectbuilding bed 2. An object is to be built on an upper surface of thisobject placement plate 11, and the space above the object placementplate 11 constitutes an object building area P₁.

[Light Beam Radiating Unit 5]

The light beam radiating unit 5 includes a light beam radiating device12 which radiates a light beam L such as a laser light. Lenses, mirrors,etc are built in the light beam radiating device 12, and the scope ofradiation of the light beam L is adjustable within a scope in thehorizontal directions (scope in X-Y axes) defined by a predetermineddistance.

[Transferring Mechanism 6]

As shown in FIG. 1 and FIG. 2, the transferring mechanism 6 comprises: apair of fixed guide rails 14 attached on the apparatus frame 9; amovable guide rail 15 which bridges between the pair of fixed guiderails 14 and is moved in the Y-axis direction by a drive source notshown; a base 16 which is attached to the movable guide rail 15 and ismoved in X-axis direction along the movable guide rail 15 by a drivesource not shown; and a support rod member 17 which is orientedvertically and is moved in

Z-axis direction relative to the base 16 by a drive source not shown.The light beam radiating device 12 is attached to the lower end of thesupport rod member 17. The above structure enables the transferringmechanism 6 to move the light beam radiating device 12 inthree-dimensional directions.

[Shroud 7]

The shroud 7 is made up of a hollow cover member with an opening formedin its lower end. In FIG. 2, it is depicted as a member of a rectangularshape, but it may be in other shapes such as a cylindrical shape. Theupper portion of the shroud 7 is attached integrally to the lower end ofthe light beam radiating device 12 so as not to interfere with theradiation area of the light beam L. The area of the opening at the lowerend of the shroud 7 is formed smaller than the object building area P₁.A skirt member 18 is provided along the periphery of the lower end ofthe shroud 7, and is movable vertically in such a manner that, whenlowered down, the skirt member 18 blocks a gap C made between the lowerend of the shroud 7 and the powder layer 13. The skirt member 18 is aframe-shaped member formed along the side surfaces of the shroud 7, andis moved up and down, for example, by a drive source such as a motorequipped on the shroud 7.

Moreover, the shroud 7 has an ambient-gas supplying port 19 forsupplying N₂ gas as an ambient gas into the inside of the shroud 7 and afume suction port 20 for suctioning a fume generated in the inside ofthe shroud 7. The ambient-gas supplying port 19 and the fume suctionport 20 are connected respectively to a N₂ gas supplying device 21 and afume suction device 22 provided outside the apparatus frame 9 viaflexible hoses 31 and 32.

[Powder Delivering Unit 3]

In FIG. 1, the powder delivering unit 3 is made up of a powder storagetank 23 with a powder dropping opening 24 formed in its lower portion.The powder storage tank 23 is formed for example in a funnel-shapehaving a hopper portion of which the cross-sectional area becomessmaller as it goes toward the powder dropping opening 24, and its upperportion is formed with an opening for filling the powder. The powder is,for example, a metal powder and the like of particle size ranging fromabout several to several tens μm. The powder storage tank 23 is equippedwith an open-close door 25 for opening and closing the powder droppingopening 24. The open-close door 25 opens and closes the powder droppingopening 24 by sliding in the lateral direction by means of a drivesource such as a motor (not shown) equipped on the powder storage tank23, for example. The powder storage tank 23 is fixed on the shroud 7 viaa bracket 26 so as to be located on a side of the shroud 7 facing in thedirection of forward movement (right direction in FIG. 1).

[Powder Flattening Device 4]

The powder flattening device 4 is made up of a blade 27 in a shape of arectangular flat plate, for example. The blade 27 is located between thepowder storage tank 23 and the shroud 7 with its plate surface extendingalong a substantially vertical direction, and smoothes the powder withits longitudinal lower edge arranged horizontally to form a powder layer13. The blade 27 is fixed either on an outer surface of the powderstorage tank 23 as shown in FIG. 1 or on an outer surface of the shroud7, by means of fastening screws or the like. The lower edge of the blade27 is at a position lower than the position of the powder droppingopening 24 of the powder storage tank 23 and the position of the lowerend of the shroud 7.

[Controller 8]

The controller 8 is composed of CPU and the like, and is located outsidethe apparatus frame 9 for example. The controller 8 controls a laserlight oscillating device 29, the N₂ gas supplying device 21, the fumesuction device 22, etc in accordance with commands from an operationalterminal device 28 such as a personal computer. The aforementioned lightbeam radiating device 12 is connected to the laser light oscillatingdevice 29 via an optical fiber cable 29.

[Explanation of Operation of Three-dimensional Object Building Apparatus1]

One example of operation of the three-dimensional object buildingapparatus 1 of above configuration will be described. FIG. 3A shows astate of the apparatus before the object building operation isinitiated, and the shroud 7 is positioned at a standby area P₂ formed atone end side of the object building area P₁. The powder dropping opening24 of the powder storage tank 23 is closed by the open-close door 25,and the skirt member 18 of the shroud 7 is uplifted. It is noted thatthe other end side of the object building area P₁ is formed as aclearance area P₃ of the powder storage tank 23.

Starting from a state shown in FIG. 3A, the open-close door 25 opens,and the shroud 7 is moved forward toward the object building area P₁ bythe transferring mechanism 6, and thereby a powder of the amountcorresponding to the moved distance is delivered on the object placementplate 11 from the powder dropping opening 24 of the powder storage tank23, and is smoothed by the blade 27 to be formed as a part of one layerof powder layer 13 below the shroud 7 (FIG. 3B). This step will bereferred to as “powder layer forming step.” It is noted that, before orafter the shroud 7 starts moving, N₂ gas is supplied into the shroud 7by the N₂ gas supplying device 21, and the fume suction device 22 isactivated to circulate the ambient gas inside the shroud 7.

Next, in order to prevent N₂ gas leakage from the gap C made between thelower end of the shroud 7 and the powder layer 13, the skirt member 18is lowered down to block the gap C as shown in FIG. 3C. It is noted thatprovision of the skirt member 18 is not necessary if the gap C is sizedsmall enough to be able to disregard the amount of N₂ gas leakage.Moreover, the gap C may be blocked by lowering down the support rodmember 17 of the transferring mechanism 6, i.e., by lowering down theshroud 7 itself, without providing the skirt member 18.

Next, a light beam L 12 is radiated from the light beam radiating deviceonto the powder layer 13, which has been smoothed in the powder layerforming step, in order to build a part of object W. This will bereferred to as “object building step.” The fume generated during objectbuilding is ejected from the fume suction port 20 by the fume suctiondevice 22.

After finishing the object building step, the skirt member 18 isuplifted, and the shroud 7 is again brought forward by transferringmechanism 6, and thereby a powder of the amount corresponding to nextobject building is delivered from the powder dropping opening 24 of thepowder storage tank 23 to an area adjacent to the already-built object Win the direction of forward movement (right side in FIG. 4A) and issmoothed by the blade 27 to form a powder layer 13 (a state of FIG. 4A).Then, the skirt member 18 is lowered down, and a light beam L from thelight beam radiating device 12 is radiated on the powder layer 13, and asubsequent part of object W is built so as to continue from the part ofobject W shown in FIG. 3C (refer to FIG. 4B). As described above, byconducting the powder layer forming step and the object building step aplurality of times, one layer of powder layer 13 of the object W isbuilt as shown in FIG. 4C. The process of building one layer of powderlayer 13 by conducting the powder layer forming step and the objectbuilding step a plurality of times will be referred to as “one layerbuilding step.”

After finishing “one layer building step,” the powder dropping opening24 of the powder storage tank 23 is closed by the open-close door 25,and the support rod member 17 is uplifted by transferring mechanism 6 bya height corresponding to the thickness of a powder layer 13 that is tobe formed subsequently, and the shroud 7 moves back to the standby areaP₂ (FIG. 5A). Then, the second powder layer 13 is formed on the firstpowder layer 13 already formed, and the one layer building step shown inFIG. 3 and FIG. 4 is conducted again. By repeating the layer buildingstep like this, building of the whole object W is completed as shown inFIG. 5B. It is noted that the shroud 7 stays in the standby area P₂ onlya short length of time, and only a slight amount of N₂ gas leaks fromthe lower end of the shroud 7. If the situation allows, the supply of N₂gas may be stopped while the shroud 7 is positioned at the standby areaP₂.

Moreover, if a three-dimensional makeshift wall 33 surrounding a spacearound the object W is built as shown in FIG. 6 in the one layerbuilding steps when the object W is built, a collapse of the powdersurrounding the object W can be prevented by the makeshift wall 33.

The advantages explained below are achieved, if the three-dimensionalobject building apparatus 1 comprises the transferring mechanism 6 whichmoves the light beam radiating device 12 (the light beam radiating unit5) in three-dimensional directions, the shroud 7 which moves integrallywith the light beam radiating device 12 and encloses a space above anarea of powder layer 13 that is smaller than the object building area P₁around radiation of the light beam L, the powder storage tank 23 (thepowder delivering unit 3) and the blade 27 (the powder flattening device4) which moves integrally with the light beam radiating device 12, asdescribed above.

(1) The size of the object W to be built can be easily enlarged up tothe three-dimensional range of movement of the transferring mechanism 6that holds the light beam radiating unit 5.

(2) The cycle time of object building can be shortened, because thepowder delivering unit 3 and the powder flattening device 4 areconfigured integrally with the light beam radiating unit 5 so that apowder layer 13 can be formed at the time of movement of the light beamradiating unit 5.

(3) The apparatus can be configured compact, because the powderdelivering unit 3 and the powder flattening device 4 are configuredintegrally with the light beam radiating unit 5 so that drive sourcesfor respective operations of the powder delivering unit 3 and the powderflattening device 4 become unnecessary.

(4) The consumption amount of the ambient gas can be reduced, becausethe ambient gas is supplied only to the inside of the shroud 7 whichcovers the powder layer 13, the area of which is smaller than the objectbuilding area P₁.

(5) Since the light beam radiating unit 5 is configured integrally withthe powder delivering unit 3 and the powder flattening device 4, thedimensional precision is improved between the light beam radiating unit5 and the surface of a powder layer 13 formed by the powder deliveringunit 3 and the powder flattening device 4. Accordingly, the focal pointof a light beam L at the powder layer 13 becomes stable, and theprecision of object building is improved.

(6) The cycle time of object building can be further shortened, becausethe object W can be built by radiating a light beam L while the lightbeam radiating unit 5 is brought by the transferring mechanism 6.

Moreover, if the powder delivering unit 3 and the powder flatteningdevice 4 are disposed on a side of the shroud 7 facing in the directionof forward movement, the powder delivering unit 3 and the powderflattening device 4 can be configured integrally with the shroud 7 witha simple structure.

Moreover, if the powder delivering unit 3 is configured as the powderstorage tank 23 with the powder dropping opening 24 at a lower portionthereof, and the powder flattening device 4 is configured as the blade27 disposed between the powder storage tank 23 and the shroud 7, thepowder delivering unit 3 and the powder flattening device 4 can beconfigured with members having simple structures and thereby can beattached to the shroud 7 easily.

Furthermore, if the open-close door 25 which opens and closes the powderdropping opening 24 of the powder storage tank 23 is provided, deliveryof the powder from the powder storage tank 23 can be easily controlledby opening and closing operation of the open-close door 25. When theshroud 7 is formed with the ambient-gas supplying port 19 and the fumesuction port 20, the ambient gas can be easily supplied to the inside ofthe shroud 7 and the fume can be easily ejected outside. Since theshroud 7 is provided with the skirt member 18, the leakage of ambientgas from the gap C made between the shroud 7 and the powder layer 13 canbe prevented efficiently.

In the above, an embodiment of the present invention has been explained.The blade 27 can be utilized as the open-close door 25 which opens andcloses the powder dropping opening 24 of the powder storage tank 23. Asshown in FIG. 7, a bearing axis 34 is provided on an outside surface ofthe powder storage tank 23, and the blade 27 is arranged so as to berotatable about the bearing axis 34. Reference numeral 35 indicates adrive source such as a motor for rotating the blade 27, which isattached to an outside surface of the powder storage tank 23 forexample. As shown FIG. 7A, the blade 27 closes the powder droppingopening 24 of the powder storage tank 23 in a state where the blade 27is oriented horizontally, and the blade 27 is rotated about the bearingaxis 34 to be oriented vertically by the driving of the drive source 35,so that the powder dropping opening 24 opens to drop and deliver thepowder, which is then smoothed by the lower edge of the blade 27.According to this structure, both powder smoothing function andopen-close function of the powder dropping opening 24 are given to theblade 27, and the configuration of the powder delivering unit 3 and thepowder flattening device 4 is simplified.

DESCRIPTION OF REFERENCE NUMERALS

-   1: three-dimensional object building apparatus-   2: object building bed-   3: powder delivering unit-   4: powder flattening device-   5: light beam radiating unit-   6: transferring mechanism-   7: shroud (a cover)-   8: controller-   11: object placement plate-   12: light beam radiating device (light beam radiating unit)-   13: powder layer-   18: skirt member-   19: ambient-gas supplying port-   20: fume suction port-   23: powder storage tank (powder delivering unit)-   24: powder dropping opening-   25: open-close door-   27: blade (powder flattening device)-   33: makeshift wall-   C: gap-   L: light beam-   P1: object building area

What is claimed is:
 1. A three-dimensional object building apparatus,comprising: a powder delivering unit that delivers a powder on an objectbuilding area; a powder flattening device that flattens the powderdelivered from the powder delivering unit to form a powder layer; alight beam radiating unit that is disposed above the object buildingarea and radiates a light beam on the powder layer to sinter or meltsolidify the powder for building an object; a transferring mechanismthat moves the light beam radiating unit in three-dimensionaldirections; a cover that moves integrally with the light beam radiatingunit and surrounds a space above an area of the powder layer that issmaller than the object building area around a radiation of the lightbeam; and wherein the powder delivering unit and the powder flatteningdevice move integrally with the light beam radiating unit.
 2. Thethree-dimensional object building apparatus according to claim 1,wherein the powder delivering unit and the powder flattening device aredisposed on a part of the cover facing in a direction of forwardmovement.
 3. The three-dimensional object building apparatus accordingto claim 2, wherein the powder delivering unit comprises a powderstorage tank with a powder dropping opening formed at a lower portionthereof, the powder flattening device comprises a blade disposed betweenthe powder storage tank and the cover.
 4. The three-dimensional objectbuilding apparatus according to claim 3, further comprising anopen-close door that opens and closes the powder dropping opening of thepowder storage tank.
 5. The three-dimensional object building apparatusaccording to claim 1, wherein the cover comprises an ambient-gassupplying port for supplying an ambient gas into an inside of the coverand a fume suction port for suctioning a fume generated in the inside ofthe cover.
 6. The three-dimensional object building apparatus accordingto claim 1, wherein, the cover is provided with a skirt member that ismovable vertically and blocks a gap made between a lower end of thecover and the powder layer when lowered down.
 7. A method for building athree-dimensional object, comprising: a step for providing a powderdelivering unit, a powder flattening device, a light beam radiating unitand a cover structured integrally with one another such that these aremovable in three-dimensional directions, wherein the powder deliveringunit delivers a powder on an object building area, the powder flatteningdevice flattens a surface of the powder delivered from the powderdelivering unit to form a powder layer, the light beam radiating unit isdisposed above the object building area and radiates a light beam on thepowder layer to sinter or melt solidify the powder for building theobject, the cover surrounds a space above an area of the powder layerthat is smaller than the object building area around a radiation of thelight beam; a one-layer building step comprising a powder layer formingstep for moving the cover in lateral direction so that a powder ofamount corresponding to the moved distance is delivered by the powderdelivering unit below the cover and flattened by the powder flatteningdevice, an object building step for radiating a light beam on the layerflattened in the powder layer forming step for building the object,wherein one powder layer is built by repeating the powder layer formingstep and the object building step; wherein the three-dimensional objectis built by repeating uplifting the cover and the one-layer buildingstep.
 8. The method for building a three-dimensional object according toclaim 7, the method comprising the step of building a three-dimensionalmakeshift wall surrounding a space around the object for preventingcollapse of the powder in the space around the object to be built.